1. Field of the Invention
The present invention relates to a data recording method, a data recording apparatus and a data recording medium suitable For recording data in an optical disk or the like.
2. Description of the Related Art
The present inventor has proposed a technique of displacing the position of the edge of each pit stepwise according to recording data, for example, in Unexamined Japanese Patent No. HEI 4-207074 and International Application No. PCT/JP92/01250. Namely, as shown in FIG. 17, each of the positions of edges b.sub.n-1, a.sub.n, b.sub.n, and a.sub.n-1 of pits is displaced to either of the positions of from 0 to 7 according to recording data. Further, as shown in FIG. 17, the level of the reproduced signal from an optical pick-up for detecting a reflection light from each pit is subjected to sample-and-hold with a timing of a rising edge of a clock A or a clock B to be analog-digital converted, so that it is possible to judge what position the edge is disposed among the position of from 0 to
Assuming that the value obtained by sampling and analog-digital converting the reproduced signal from the edge a.sub.n is taken as Va(n) and the value obtained by sampling and analog-digital converting the reproduced signal from the edge b.sub.n is taken as Vb(n), the values Va(n) and Vb(n) are expressed on XY coordinate axes as shown in FIG. 18. As the positions of the edges a.sub.n and b.sub.n are displaced into the positions of from 0 to 7, the points (information points) specified by the reproduced values Va(n) and Vb(n) are ideally positioned at the points (grids) where dotted lines are crossed to each other in FIG. 18. In practice, however, the edge b.sub.n interferes with the reproduced signal from the edge a.sub.n, or the edge an interferes with the reproduced signal from the edge b.sub.n. As a result, the positions of the information points (in FIG. 18, shown as black dots) specified by the level of the actual reproduced signals are deviated from the grids.
For this reason, in the previous application described above, under consideration of the deviation of the information point from the grid, the present inventor has proposed such a technique that, the position of the information point (position of the edge) on the coordinate axes is read-out as the position on the coordinate plane.
As described above, in the previous proposal technique, only the I. S. I (Inter Symbol Interference) between two edges has been examined; however, actually, there occurs the I. S. I between three or more edges. As a result, as shown in FIG. 19, the area of each information point on the coordinate axes is broadened, and the boundary between the adjacent information points is made obscure, which makes it difficult to discriminate each information point. (Namely, it is difficult to enhance the recording density).